I'll leave the model discussion to a Rolls Expert. The film setting is summer 1973. (Hence the F-plate ?)
The Rolls is a character car in that the audience knows its Kendrick's status symbol, and a feature of the dialogue in Freddie Taylor's insurance job interview with Mr Kendrick at the start of the film (~along with the ú42,000 house!).
I think its driven at the company dinner-dance as well as parked outside the mansion.